Method for determining resources of physical downlink control channels

1. A method, in a UE or an eNB, of determining resources to be decoded by the UE to retrieve physical downlink control channels, comprising:

determining a start position of a unit of resources in one physical resource block pair according to UE specific information;

determining a gap between two of the units; and

determining a set of units, in a given plurality of physical resource block pairs, according to said start position and said gap, as the resources to be decoded,

wherein the gap between two of the units is not an integer-multiple of the size of one of the physical resource block pairs.

2. The method according to claim 1 , wherein, said unit is a control channel element within a physical resource block, and said determining a start position of a unit of resources in one physical resource block pair according to UE specific information includes determining the start position of a control channel element in one physical resource block pair according to:

the total number of control channel elements that is required in the physical downlink control channel; and

the number of control channel elements in one physical resource block pair.

3. The method according to claim 2 , wherein said determining a start position of a unit of resources in one physical resource block pair according to UE specific information includes using the following equation:

I ECCE =max[ ID C-RNTI mod( N ECCE −( AL− 1)),0]

wherein, I ECCE stands for the index of the start control channel element in one physical resource block pair, ID C-RNTI stands for a UE-specific ID, N ECCE stands for the number of control channel elements in one physical resource block pair, and AL stands for the aggregation level that is relevant with the total number of control channel elements that is required in the physical downlink control channel.

4. The method according to claim 1 , wherein the unit of the resources is a resource element group within a control channel element in a physical resource block pair, and said determining a start position of a unit of resources in one physical resource block pair according to UE specific information comprises:

determining the start position of a control channel element, within which the resource element group is located, in one physical resource block pair according to:

UE specific information;

the total number of control channel elements that is required;

the number of resource element groups in one control channel element; and

the number of control channel elements in one physical resource block pair

determining the start position of the resource element group in the control channel element according to:

UE specific information;

the total number of control channel elements that is required; and

the number of resource element groups in one control channel element.

5. The method according to claim 4 , wherein said determining the start position of a control channel element, within which the resource element group is located, in one physical resource block pair includes using the following equation:

I

ECCE

=

max

⁡

[

ID

C

⁢

-

⁢

RNTI

⁢

mod

⁡

(

N

ECCE

-

(

⌊

AL

N

EREG

⌋

-

1

)

)

,

0

]

wherein, I ECCE stands for the index of the start control channel element in one physical resource block pair, ID C-RNTI stands for a UE-specific ID, N ECCE stands for the number of control channel elements in one physical resource block pair, N EREG stands for the number of resource element groups within one control channel elements, and AL stands for the aggregation level that is relevant with the total number of control channel elements that is required in the physical downlink control channel.

6. The method according to claim 4 , wherein said determining the start position of the resource element group in the control channel element includes using the following equation:

I EREG =max[ ID C-RNTI mod( N EREG −( AL− 1)),0]

wherein, I EREG stands for the index of the start resource element group within one control channel elements, ID C-RNTI stands for a UE-specific ID, N EREG stands for the number of resource element groups within one control channel elements, and AL stands for the aggregation level that is relevant with the total number of control channel elements that is required in the physical downlink control channel.

7. The method according to claim 1 , wherein said determining a start position of a unit of resources in one physical resource block pair according to UE specific information includes determining the start position of a unit of the resources in one physical resource block pair further according to at least one of:

the index of the sub-frame for the physical downlink control channel;

the physical resource block pairs for the physical downlink control channel.

8. The method according to claim 1 , wherein said unit is a control channel element within a physical resource block pair, and

said determining a gap between two of the units comprises:

determining the gap between two of the control channel elements; or

determining the control channel elements within the same physical resource block pair as being contiguous.

9. The method according to claim 1 , wherein the unit of the resources is a resource element group within a control channel element in a physical resource block pair, and said determining a gap between two of the units comprises:

determining the resource element groups within the same control channel element as being contiguous;

determining the gap between corresponding resource element groups within different physical resource block pairs according to:

the number of control channel elements in one physical resource block pair;

the total number of physical resource block pairs available for the physical downlink control channel; and

the number of physical resource block pairs into which the physical downlink control channel is to be spread.

10. The method according to claim 9 , wherein said determining a gap between two of the units includes using the following equation to determine the gap between corresponding resource element groups within different physical resource block pairs:

G

EREG

=

⌊

(

N

ECCE

×

N

PRB

)

N

DIV

⌋

wherein, G EREG is the gap in a unit of control channel element, N ECCE stands for the number of control channel elements in one physical resource block pair, N PRB stands for the total number of physical resource block pairs available for the physical downlink control channel, and N DIV stands for the number of physical resource block pairs into which the physical downlink control channel is to be spread.

11. The method according to claim 1 , wherein the method is in a UE for retrieving the physical downlink control channel, the method further comprising:

determining one or more candidates in said plurality of physical resource block pairs, based on the determined set;

for a respective candidate, decoding the signal transmitted on the set of units of resources for that candidate, for retrieving the physical downlink control channel from that candidate.

12. The method according to claim 1 , wherein the method is in an eNB for transmitting the physical downlink control channel, the method further comprising:

determining one or more candidates in said plurality of physical resource block pairs, based on the determined set;

selecting one from the one or more determined candidates, and transmitting the encoded physical downlink control channel in the selected candidate.

13. An apparatus, in a UE or an eNB, for determining resources to be decoded by the UE to retrieve physical downlink control channels, comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform:

determining a start position of a unit of resources in one physical resource block pair according to UE specific information;

determining a gap between two of the units;

determining a set of units, in a given plurality of physical resource block pairs, according to said start position and said gap, as the resources to be decoded;

wherein the gap between two of the units is not an integer-multiple of the size of one of the physical resource block pairs.